1. Field of the Invention
The invention relates to a signal transmission system which is suitable when it is used for charging and discharging a battery pack and to a battery pack.
2. Description of the Related Arts
In recent years, a chargeable battery pack has been used in a cellular phone and a VTR integrated type digital camera (hereinafter, they are generally referred to as electronic apparatuses). The battery pack is constructed by a secondary battery and used in a state where it is built in the electronic apparatus or in a removable state. In a state where the battery pack is attached to the electronic apparatus, the battery pack can be charged. In addition to the secondary battery, a protecting circuit is provided for the battery pack. A circuit for detecting a voltage, a current, and a temperature of the secondary battery and the like are provided for the protecting circuit.
There is a case where, for example, when a chain short-circuit occurs, the secondary battery overheats and a heat generation of the secondary battery occurs. In the worst case, there is a case where a fire occurs due to the chain short-circuit as a cause. Therefore, to prevent the overheat of the secondary battery, the protecting circuit for detecting the voltage, current, and temperature is provided for the battery pack.
For example, as shown in FIG. 1, the battery pack is constructed by terminals T1, T2, and T3, a detecting circuit 71, a detecting and control circuit 72, a switching circuit SW, and a secondary battery BT. The detecting circuit 71 detects impedances of an electronic apparatus and a charging device to which the battery pack is connected. The detecting and control circuit 72 detects a terminal voltage, a current, and a temperature of the secondary battery BT. The on/off operations of the switching circuit SW are controlled in accordance with the detected terminal voltage, current, and temperature. For example, when an overcharge is detected, the switching circuit SW is turned off.
In recent years, as shown in FIG. 2, there is a method of detecting an impedance connected to the battery pack and controlling the protecting circuit. In FIG. 2, the battery pack BP is constructed by terminals T11, T12, and T13, a signal receiving and transmitting circuit 211, a detection control circuit 212, the switching circuit SW, and the secondary battery BT. An impedance 213 is connected through the terminals T11 and T12. An impedance 214 is connected through the terminals T12 and T13. When the impedance 213 or 214 is connected, a signal which is obtained from the connected impedance 213 or 214 is received by the signal receiving and transmitting circuit 211. The received signal is supplied from the signal receiving and transmitting circuit 211 to the detection control circuit 212. The detection control circuit 212 detects a temperature and a terminal voltage and/or a current of the secondary battery BT. The detection control circuit 212 controls the switching circuit SW in accordance with the detected temperature, terminal voltage, and/or current of the secondary battery BT and with the supplied signal.
According to the protecting circuit of a type such that the impedance connected to the battery pack is detected and the switching circuit is controlled as mentioned above, there is a problem such that a residual voltage, a residual current, and a temperature of the secondary battery BT cannot be communicated (transmitted) with (to) an external electronic apparatus or charging device.
According to the method of detecting the impedance and controlling the protecting circuit as mentioned above, there is also a problem such that the signal can be transmitted only upon charging or upon discharging. Further, there is a problem such that a use range is narrow.
Assuming that the signal to be transmitted is a digital signal, there is a problem such that the circuit is expensive. Hitherto, since a power source at the time when the signal is transmitted from the battery pack to the outside is obtained from the secondary battery included in the battery pack, there is also a problem such that when a voltage of the secondary battery drops, the digital signal cannot be outputted and the electronic apparatus cannot be controlled.
On the other hand, in order to output the signal even if the voltage of the secondary battery drops, since terminals for supplying the power source are necessary, there is also a problem such that at least four terminals are necessary.
It is, therefore, an object of the invention to provide a battery pack which can communicate with an external electronic apparatus or charging device.
Another object of the invention is to provide a signal transmission system and a battery pack, in which a power source is supplied from an outside through three terminals and a signal can be transmitted to the outside even upon charging and discharging.
According to the first aspect of the invention, there is provided a battery pack using a secondary battery, comprising: at least first, second, and third terminals; signal transmitting means for transmitting a signal from one of the first, second, and third terminals; first detecting means for detecting a first device connected to the first and second terminals and a second device connected to the second and third terminals; second detecting means for detecting a temperature, a voltage, and/or a current of the secondary battery; and control means for turning on switching means when the first or second device is detected by the first detecting means and turning off the switching means when the first or second device is not detected by the first detecting means.
When one of the first device (electronic apparatus) and the second device (charging device) is connected and it is detected that the first or second device has been connected, the switching means is turned on. When it is detected that the first or second device is disconnected, the switching means is turned off. The signal is transmitted from at least one of the first, second, and third terminals.
According to the sixth aspect of the invention, there is provided a signal transmission system for transmitting a signal from a battery pack to an outside, wherein the battery pack comprises: first, second, and third terminals; a secondary battery and switching means which are serially connected between the first and second terminals; power forming means for forming a predetermined power source from a power source which is supplied through the first or second terminal and the third terminal; signal transmitting means for transmitting a signal which is formed by the power source which is supplied from the power forming means through the first or second terminal and the third terminal; and control means for controlling the switching means, and a charging device obtains the power source which is supplied to the battery pack through the first or second terminal and the third terminal from a commercially available power source.
According to the tenth aspect of the invention, there is provided a battery pack comprising: first, second, and third terminals; a secondary battery and switching means which are serially connected between the first and second terminals; power forming means for forming a predetermined power source from a power source which is supplied through the first or second terminal and the third terminal; signal transmitting means for forming a signal by the power source which is supplied from the power forming means and transmitting the formed signal through the first or second terminal and the third terminal; and control means for controlling the switching means.
As mentioned above, the charging device and the battery pack are connected through the three terminals, the power source which is formed from the commercially available power source by the charging device, and the signal can be transmitted to the outside by the supplied power source.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.